This invention relates to the molding and application of protective caps to microelectronic semiconductor chips on a wafer scale as opposed to application on an individual chip basis. More particularly the invention relates to the molding and application of protective caps to semiconductor chips incorporating light emitting devices.
Semiconductor chips are normally packaged in a protective layer or layers to protect the chip and its wire bonds from atmospheric and mechanical damage. Existing packaging systems typically use epoxy molding and thermal curing to create a solid protective layer around the chip. This is normally carried out on individually diced chips bonded to lead frames and so must be done many times for each wafer. Alternative methods of packaging include hermetically sealed metal or ceramic packages, and array packages such as ball grid array (BGA) and pin grid array (PGA) packages. Recently wafer scale packaging (WSP) has started to be used. This is carried out at the wafer stage before the chips are separated. The use of molding and curing techniques subjects the wafer to both mechanical and thermal stresses. In addition the protective cap so formed is a solid piece of material and so cannot be used for MEMS devices, since the MEMS device would be rendered inoperable by the polymer material. Existing packaging systems for MEMS devices include thematically sealed packages for individual devices, or use silicon or glass wafer scale packaging, both of which are relatively high cost operation.
Devices which incorporate optically active devices, such as light emitting devices or photoreceptors, also require a cap with at least a portion of the cap transparent to the relative light. The caps also frequently require a lens to focus light passing through the cap and so the epoxy molding techniques cannot be used. The devices are typically packaged individually or use silicon or glass wafer scale packaging.
In one broad form the invention provides a light emitting semiconductor package including:
a) a chip having a top surface and a bottom surface and having at least one light emitting semiconductor device which emits electromagnetic radiation at one or more wavelengths from the top surface;
b) a first hollow molded cap having a central portion and a first perimeter wall extending from the perimeter of the central portion with the free edge of the first perimeter wall bonded to the top surface to provide a first cavity and which, in plan view, overlays part or all of at least one light emitting device, said central portion including at least one region which is at least substantially transparent or translucent to electromagnetic radiation at said one or more wavelengths; and
wherein the first cap has been bonded to the semiconductor chip at the wafer stage prior to separation of the wafer into individual packages.
The at least one region may also refract the electromagnetic radiation emitted by said one at least one device.
The cap may also include at least one attachment means for attaching an electromagnetic radiation transmitting cable or fiber to the cap, whereby electromagnetic radiation emitted from the at least one device passes through the at least one region into the cable. The at least one attachment means is preferably a second perimeter wall extending from the periphery of the central portion away from the first perimeter wall or at least one recess in the central portion.
The package may also include a second cap bonded to the bottom surface of the chip.
The second cap may, in plan view, overlay part or all of the one or more devices.